The present invention relates to measuring instruments, and more particularly concerns measurements of the position of a pipe centerline. In U.S. Pat. No. 3,944,798, of Homer L. Eaton, there is disclosed a method and apparatus for measuring position and direction of a pipe centerline by use of a five axis articulated arm, bearing at the free end of the outermost arm a V-shaped working head or probe which may be moved to a number of diverse positions and orientations to contact a pipe upon which measurements are to be made. In general, for measurement of bent pipe, and for bending pipe, it is important to know various parameters, including the length of the pipe straight portions or distance between bends (DBB), the bend angle or degree of bend (DOB), and the plane of the bend angle or plane of bend (POB). By locating vectors lying along the centerlines of the pipe straight portions, the required parameters can be readily calculated. Thus, in order to obtain the necessary information or data to define a bent pipe and its several bends, it is only necessary to obtain data defining the position and orientation of the centerlines of the respective straight sections of the pipe. The position and direction of these vectors can be obtained either by measuring position of two points on each vector, thus defining the vector, or by use of the instrument of U.S. Pat. No. 3,944,798, which enables measurement of the direction of the vector by a single contact between the V-shaped working head and the exterior of the pipe.
The contact probe, or working head, of the pipe of the U.S. Pat. No. 3,944,798 has four contact elements which are positioned so that all of these elements will make electrical contact with the outer surface of the pipe, and thus signify obtaining of a desired relative position and orientation of the pipe centerline with respect to the working head. All of the electrical contact elements must contact the pipe, and thus some time and effort is involved in manipulation of the working head to ensure appropriate contact and appropriate orientation of the working head. This slows the making of the many measurements that are required for defining adequate data for a complete set of pipe bends.
Another problem with the contact probe of the Eaton patent is that the required contact between the probe and some slender, flexible pipes may result in distortion of the pipe, and thus create an erroneous reading of either pipe centerline position or direction. Therefore, in making measurements of very small diameter, slender and somewhat flexible pipes the contact probe of the prior art must be used at an even slower pace and with even greater degree of care to avoid distortion of the pipe by the necessary contact, and thus to avoid erroneous read out.
Accordingly, it is an object of the present invention to provide a pipe measuring probe which avoids or minimizes above-mentioned problems.